1. Field of the Invention
The present invention relates to the methods of collecting airborne particles and microorganisms. In particular, the invented apparatus relates to the method of collecting aerosol particles by injecting them into a swirling air flow so that they are removed from the suspending air onto the surface over which the flow swirls.
2. Description of the Related Art
Devices collecting airborne particles and microorganisms for measurement or control purposes commonly remove the particles and microorganisms by inertial impaction, centrifugal removal or impingement into a liquid. Particles or microorganisms suspended in air are herein referred to as "aerosol particles." In inertial impaction, the aerosol particles are drawn into a nozzle which is directed toward a solid plate; aerosol particles with high inertia impact onto the plate and are collected by it. The embodiment of this method is usually referred to as an "inertial impactor." A common problem with the impactor is the bounce of particles from the surface when the force of particle rebounding exceeds the particle adhesion force.
Another method is that of aerosol particle removal by centrifugal force. The embodiment of this method is usually referred to as a "cyclone." In a cyclone, the aerosol is drawn into a cylindrical chamber so that the air makes one or more rotations inside before leaving the chamber through a tube at its center. Particles with sufficient inertia move centrifugally toward the inner wall. The problem with this method is that particles that enter the cyclone near its inner effluent tube have a great radial distance to traverse. This method is, therefore, not effective for particles less than a few micrometers in diameter. Also, it does not provide a sharp particle size separation between the collected and uncollected particles.
A third method is that of aerosol particle impaction into a liquid. The embodiment of this method is usually referred to as an "impinger." In an impinger, the aerosol is impacted into a reservoir filled with liquid. The problem with this method is that the air flow produces bubbling in the liquid reservoir through which already collected particles may be reaerosolized into the effluent air flow. An impinger is commonly used only with liquids having the viscosity and surface tension characteristics of water or similar liquids.